1. Field of the Invention
The invention relates generally to the field of film unwinding apparatus, and in particular to unwinding apparatus that can disengage a trailing film end from a film spool.
2. Description of the Prior Art
Commonly assigned U.S. Pat. No. 5,031,852, issued Jul. 16, 1991 discloses a film cassette wherein a film roll whose outermost convolution is a film leader is coiled about a spool core rotatable within the cassette shell in film unwinding and winding directions. A pair of flexible flanges are coaxially arranged on the spool core to radially confine the film leader within respective skirted peripheries of the flanges to prevent the leader from clock-springing against an interior wall of the cassette shell. A film stripper projects from the interior wall to be received between a leading end portion of the film leader and the next inward convolution of the film roll to free the leader from the flanges and guide it into a lighttight passageway to the exterior of the cassette shell responsive to rotation of the spool core in the unwinding direction. Thus, when the spool core is rotated in the unwinding direction, the film leader will be thrust or propelled from inside to outside the cassette shell.
Various means such as tape or a fastening hook may be devised for attaching an inner or trailing end portion of the film roll to the spool core. However, such known means have been found not to work well in the film cassette.
3. The Cross-Referenced Application
Cross-referenced application Ser. No. 07/793,980 discloses a film cassette wherein a spool core about which a filmstrip is coiled is rotated in an unwinding direction to thrust a leading end portion of the filmstrip from inside to outside the cassette. The filmstrip has a trailing or inner end portion with a hole in it. The spool core includes a double-hook piece in the hole having a shorter hook and a longer hook. The shorter hook projects from the hole in the unwinding direction to slightly overlie the trailing end portion to engage the trailing end portion for pushing the filmstrip off the spool core to thrust the leading end portion outside the cassette when the spool core is rotated in the unwinding direction, but which will exit the hole as the trailing end portion begins to separate from the spool core. The longer hook projects from the hole in a winding direction to substantially overlie the trailing end portion to engage the trailing end portion for preventing the trailing end portion from completely separating from the spool core when the shorter hook is removed from the hole, but which can be backed out of the hole by rotating the spool core relative to the trailing end portion in the unwinding direction.
Since the shorter hook and the longer hook can each be disengaged from the trailing end portion of the filmstrip without damaging the filmstrip, the filmstrip can be completely removed from the film cassette for processing or other purpose and then returned to the cassette to be re-engaged with the hooks. Thus, the processed film can be stored in the cassette.